The present invention relates to a modified starch which is prepared by hydrolysis of a starch molecule using glucoamylase after the preparation of a starch derivative containing a hydrophobic group or both a hydrophobic and a hydrophilic group. Such modified starch is useful as an emulsifying agent or as an encapsulating agent, particularly in systems where high load and retention of the active ingredient, low surface oil exposure, and excellent oxidation resistance is desired.
U.S. Pat. Nos. 4,977,252 and 5,185,176 issued to Chiu disclose starch derivatives containing a hydrophobic or both a hydrophobic and a hydrophilic group which have been enzymatically degraded by exo-enzymes which exhibit selectivity in cleaving the 1,4-linkages and leaving the 1,6-linkages intact. These modified starches are useful as emulsifiers.
A variety of chemical compositions are conventionally used as encapsulating agents in, inter alia, the food, cosmetic, paint, pharmaceutical, personal care, and polymer industries. Typical compositions which conventionally function as encapsulating agents include gum arabic, dextrins, low viscosity modified starches, arabinogalactan, gum acacia, casein, gelatin, carboxymethyl cellulose, and tragacanth, karaya, sodium alginate, tannin, and celluloses.
These typical compositions however do not consistently provide high active agent loading and retention, low surface oil and excellent oxidation resistance. In general, powders prepared with conventional encapsulating agents do not contain a high level of active agents. When loaded with oil levels of higher than 15-20%, such conventional encapsulated powders lose a considerable amount of the oil during the drying process, have much of the oil exposed on the surface of the powder, and/or generally have poor oxidation resistance.
U.S. Pat. No. 3,971,852 issued to Brenner, et al. discloses a method for encapsulating oils in particles of a solid water-sensitive, preferably water-soluble, protective matrix that isolates the oils until they are released for use by exposure of the particles to moisture. The matrix-forming encapsulation materials include mixtures of polysaccharides and polyhydroxy compounds that can form aqueous emulsions with the oil. Although the patent claims efficient encapsulation of up to 80% by volume and surface oil not substantially above 5%, with a relatively high loading, the known process fails to provide efficient encapsulation oil recovery with excessive oil loss during drying and extractable oils as high as 10-24% when the encapsulated oil content exceeds 60% by weight. Furthermore, it has not been shown that these matrices provide good oxidation resistance.
U.S. Pat. No. 5,087,461 issued to Levine, et al. discloses a spray dried composition encapsulated in an extruded glassy matrix composed of a chemically modified starch having a dextrose equivalent no greater than 2, a maltodextrin, a corn syrup solid or polydextrose, and a mono- or di-saccharide. However, these encapsulated products are unable to achieve high loading and are susceptible to oxidation.
EP Patent Application No. 550 067 Al discloses a method for encapsulating oils in a water-sensitive cellular solid matrix by drying an aqueous emulsion containing the oil to be encapsulated, a non-crosslinked lipophilically modified starch that undergoes crosslinking during drying, and a polyhydroxy compound that forms with the polysaccharide material a continuous aqueous phase in which the oil is dispersible as a discontinuous phase. This method of encapsulation is unacceptable for foods and pharmaceuticals and requires the incorporation of a silicone-based material which is difficult to process using conventional methods. Furthermore, it has not been shown that these matrices provide good oxidation resistance.
However, none of the encapsulating agents known in the art provide a high load of at least 40% while maintaining a retention of at least 90% of the active ingredient with less than 3% surface oil exposure, and excellent oxidation resistance for a wide variety of encapsulating agents. Surprisingly, it has now been discovered that the present invention which uses a modified starch, prepared by enzymatically converting a starch using glucoamylase after the preparation of a starch derivative containing a hydrophobic group or a hydrophobic and a hydrophilic group, as an encapsulating agent, may consistently allow for such high load and retention of a variety of active ingredients and low oil exposure while providing excellent oxidation resistance. Further, such glucoamylase degraded starch derivatives are excellent emulsifiers.